The research objective of this proposal is to construct a metabolic model of the uterine factors which contribute to the mechanisms underlying nidation in the rat. The specific aim of the proposal is to examine three aspects of the progestational physiology of the endometrium: activity of the "pentose-shunt"; protein synthetic capabilities, and glycogen metabolism. It is expected that the results of this project will lead to a definition of the mechanism of nidation and its endocrine control, and the construction of at least one model of the mechanism, aspects of which may be tested in other mammals, including man. At the present time, a metabolic model of progestation has been formulated, based upon estrogen-progestogen interaction on pentose- shunt subsequent changes in nucleic acid and protein in endometrium during the first few days of progestation leading up to implantation and decidual sensitivity.